SENSE OF SMELL IN DOGFISH. 



65 



fering \\-ith one or other of the nasal organs. This might be accomplished by cutting 

 the olfactory tracts of one side or by temporarily occluding one of the nasal apertures. 

 Fish in which the olfactory tracts have been cut rarely live more than a few days after 

 the operation. The}' are apparently very susceptible to infection from cuts made in 

 the ^^ci^ity of the brain. I therefore abandoned this method of procedure and adopted 

 that of filling the nostrils with cotton wool. But even this method is not without its 

 defects. If a single nostril cavity is plugged tightly with cotton the fish will often fail 

 to respond to the presence of food precisely as it does when both are filled. On removing 

 the cotton from such cavities they are generally found to be inflamed, if not suppurated, 

 showing that their surfaces are decidedly delicate. None of these complications arise 

 when the nasal cavity is only lightly filled with cotton and yet this method seems to be 

 effective in checking the currents of water through the nose. I therefore adopted a 

 light plug of cotton wool as a means of excluding the action of a g^ven nasal organ. 



To ascertain the state of the normal dogfish, records were taken of the direction 

 of the head movements, to the right and to the left, in response to the presence of bait, 

 and of the time consumed between the moment when the packet of crab meat was 

 first scented by the dogfish and when it was finally seized and carried off. These records 

 served as a basis for comparison with the reactions of fish especially prepared for tests. 

 The records of the normal fish are given in table i. 



T.\Bi,E I. — Records from Five Normal Dogfish. 



From table i it will be seen that the dogfish tested found the bait in a little over 

 an average of two minutes and that they accomplished this operation by making about 

 as many right-handed as left-handed movements. Many of their movements were 

 combined and resulted in more or less continuous and characteristic courses in the 

 form of a figure eight. 



In a second series of tests dogfish in which the left nostrils had been lightly filled 

 with cotton were subjected to the same conditions as were the normal fish whose reac- 

 tions are recorded in the preceding table. The records of five of the fish with the left 

 nostrils occluded are given in table 2. 



